1. Field of the Invention
The present invention relates to a fingerprint reading device and to a method of use thereof.
2. Related Background Art
Some known systems for authenticating an individual for the purpose of keeping confidentiality, etc., use an ID number, a password, and so on. However, an ID is not perfect to maintain confidentiality because the ID number and password might leak out. While on the other hand, a system using a fingerprint reading device is proposed as being capable of keeping confidentiality at a much higher level.
There have been proposed electrostatic capacity type fingerprint reading devices (Japanese Patent Application Laid-Open No. Hei4-231803, etc.) for detecting a fingerprint pattern by utilizing the fact that electrostatic capacities between a group of electrodes arranged in a two-dimensional array and a finger touching [on] the electrode group through a dielectric substance layer differ corresponding to a ruggedness of the fingerprint. Some of this type of fingerprint reading devices has been utilized.
However, because the electrostatic capacity type fingerprint reading sensor in the prior art has a necessity for providing detection electrodes and active elements in a two-dimensional array, it is complicated in manufacturing and high in Cost. Further, conventionally there was not a well-designed scheme for what sort of apparatus incorporate such type of fingerprint reading device and how the fingerprint reading device is used, and very few fingerprint reading devices have been utilized.
It is a primary object of the present invention, which was devised under such circumstances, to provide a finger print reading device and a method thereof that are capable of enhancing a versatility when actually used, increasing productivity and reducing costs.
To accomplish the above object, according to a first aspect of the present invention, a fingerprint reading device comprises a fingerprint reading sensor including a group of first electrodes arranged in a plurality of lines extending in a first direction, a group of second electrodes arranged in a plurality of lines extending in a second direction intersecting the first direction above the first electrode group through an inter-layer insulating film, and a surface protective film composed of a dielectric substance provided on the second electrode group, and a drive circuit for measuring an electrostatic capacity between each of the electrodes and a fingerprint touching on the surface protective film by sequentially applying a predetermined voltage to any one group of the first electrodes and the second electrodes and at the same time sequentially applying the voltage to the other group of the electrodes, and measuring a change in the electrostatic capacity in the vicinity of a point of intersection between the first electrode and the second electrode.
According to the first aspect of the invention, the predetermined voltage is applied to every first electrode, and the pattern of the electrostatic capacities at the points of intersections are detected by scanning the second electrodes, thereby obtaining an image of the fingerprint.
According to a second aspect of the present invention, in the fingerprint reading device according to the first aspect of the invention, the drive circuit may detect, as a first electrostatic capacity value, the electrostatic capacity between each of the electrodes and the fingerprint touching on the surface protective film in a state where the voltage is applied to each electrode of the first electrode group and of the second electrode group, and further detect, as a second electrostatic capacity value, the electrostatic capacity between each of the electrodes and the fingerprint touching on the surface protective film in a state where the voltage is applied simultaneously to two electrodes passing through each point of intersection between the first electrode and the second electrode, then obtain an electrostatic capacity variation value at each point of intersection by comparing the first electrostatic capacity value with the second electrostatic capacity value, and obtain a fingerprint pattern from a pattern of the electrostatic capacity variation values.
According to the second aspect of the invention, the first electrostatic capacity value between the fingerprint and the electrode when applying the voltage solely to each of the first and second electrodes, is compared with the second electrostatic capacity value when applying the voltage simultaneously to the first and second electrodes passing through each point of intersection, thereby obtaining the electrostatic capacity variation values between the respective points of intersections and the fingerprint. A fingerprint pattern is obtained from the pattern of the electrostatic capacity variation values.
According to a third aspect of the present invention, in the fingerprint reading device according to the first or the second aspect of the invention, the fingerprint reading sensor may be transparent and provided in at least a part of the display area of the liquid crystal panel of the liquid crystal display device.
According to the third aspect of the invention, the fingerprint reading sensor is provided in superposition on the display area of the liquid crystal panel, and can be therefore mounted together with the liquid crystal panel when incorporating into an electronic apparatus, etc. This makes it feasible to save space for installing the fingerprint reading sensor.
According to a fourth aspect of the present invention, in the fingerprint reading device according to the third aspect of the invention, the fingerprint reading sensor may be provided on a surface of the polarizing plate or the transparent substrate of the liquid crystal panel.
According to the fourth aspect of the invention, the fingerprint sensor is provided on the transparent substrate or the polarizing plate and can thus be made integral with the liquid crystal panel.
According to a fifth aspect of the present invention, a fingerprint reading method comprises the steps of arranging a group of first electrodes in a plurality of lines extending in a first direction, arranging a group of second electrodes in a plurality of lines extending in a second direction intersecting the first direction above the first electrode group through an inter-layer insulating film, applying sequentially a predetermined voltage to any one group of the first electrodes and the second electrodes and at the same time sequentially applying the voltage to the other group of the electrodes by use of a fingerprint reading sensor of which a surface is provided with a surface protective film composed of a dielectric substance, and measuring a change in electrostatic capacity at a point of intersection between the first electrode and the second electrode.
According to the fifth aspect of the invention, the predetermined voltage is applied to every first electrode, and the pattern of the electrostatic capacities at the points of intersections are detected by scanning the first electrodes, thereby obtaining an image of the fingerprint.
According to a sixth aspect of the present invention, a fingerprint reading method comprises the steps of detecting, as a first electrostatic capacity value, the electrostatic capacity between each of the electrodes and the fingerprint touching on the surface protective film in a state where the voltage is applied to each electrode of the first electrode group and of the second electrode group, detecting, as a second electrostatic capacity value, the electrostatic capacity between each of the electrodes and the fingerprint touching on the surface protective film in a state where the voltage is applied simultaneously to two electrodes passing through each point of intersection between the first electrode and the second electrode, obtaining an electrostatic capacity variation value at each point of intersection by comparing the first electrostatic capacity value with the second electrostatic capacity value, and obtaining a fingerprint pattern from a pattern of the electrostatic capacity variation values.
According to the sixth aspect of the invention, the first electrostatic capacity value between the fingerprint and the electrode when applying the voltage solely to each of the first and second electrodes, is compared with the second electrostatic capacity value when applying the voltage simultaneously to the first and second electrodes passing through each point of intersection, thereby obtaining the electrostatic capacity variation values between the respective points of intersections and the fingerprint. A fingerprint pattern is obtained from the pattern of the electrostatic capacity variation values.